1. Field of the Invention
The present invention relates to a connector system that is board mounted so as to be connectable to planar pads provided in an area array on a surface of the circuit board.
2. Description of the Prior Art
Advances in the computational power of integrated circuitry have proceeded to the extent where the perimetrical dimensions of the circuit board on which the integrated circuitry is disposed afford insufficient space for the required number of input/output planar pads. In response board designers have located planar pads for input/output lines on interior regions of the surface of the board. Such an arrangement of planar pads is known in the art as an area array. Interconnection to the planar pads in an area array may be afforded in a variety of ways.
One typical expedient is the use of a surface mounted connector which is individually welded to the planar pads in the area array. However, this arrangement is believed conveniently useful only for an area array of two rows. Extensions of such arrangements to higher densities is made difficult due to solder reflow and/or inspection problems.
Another expedient involves the use of a flexible circuit itself having electrical contact pads formed thereon. The pads are biased into contact with the contact points in the area array by a biasing member (e.g., an elastomeric spring). The spring member is secured to the appropriate area of the board by a suitable support system.
The use of the flexible circuit laminants as the direct to-the-board interconnect element is believed beneficial for a number of reasons. The use of such laminants, due to the imaging process that is used to produce them, allows for a greater degree of interconnect density than is normally achievable with the more standard stamped metal and plastic housing connector systems. The laminants can be designed to assure the electrical integrity of the signal that is being transmitted over the connection. Requirements such as matched impedance and shielding are also readily achievable within printed circuit technology.
Moreover, such laminants are used in TAB (tape automated bonding) technology. Increasing numbers of chips and dies are being terminated to flexible circuit substrates due to the accuracy and increased density that can be achieved using TAB technology. TAB manufacturing also allows for better economic manufacturing processes.
The number of chips and or dies that can be mounted to the flexible circuit is strictly a function of the design of the circuit itself. Chips and dies may be mounted on both sides of the flexible circuit. The circuit itself can be a single layer circuit or a multi-layer circuit. The contact pad pattern can be any design consistent with a user's requirements. The density and design of the pattern of contact pads is only limited by the user's design and by the dimensional tolerances associated with properly locating the pad pattern on the flexible circuit with the pattern of planar pads on the board. The contact pads on the flexible circuit (or the planar pads on the board) may be dimpled, if necessary, in order to take advantage of the concentration of Hertzian stress that such point-to-point contact would produce. The flex circuit design can be customized for each application depending upon what function is required.
In view of the foregoing it is believed advantageous to provide a modularized interconnect system using a flexible circuit as the interconnect element whereby electrical contact with the planar pads in the area array on the surface of a board may be effected.